The present disclosure relates to a radio frequency switch circuit that may be applied to a communications system.
Generally, a semiconductor integrated circuit embedded in a communications system includes a radio frequency switch circuit controlling a transfer path of a radio frequency signal between an antenna and a transmitting unit/receiving unit.
The radio frequency switch circuit may be used in communications systems, such as Bluetooth, cellular personal communications services (PCS), code division multiple access (CDMA), wideband code division multiple access (WCDMA), time division multiple access (TDMA), global system/standard for mobile communications (GSM), and the like, as well as a wireless local area network (WLAN).
Usually, the radio frequency switch circuit may be used between a transmitting unit and a receiving unit in various communications systems using time-division multiplexing (TDM). Since the transmitting unit and the receiving unit are alternately turned on and turned off by using the radio frequency switch circuit, overall power consumption of a communication system may be decreased, and interference between the transmitting unit and the receiving unit may also be decreased.
An existing radio frequency switch circuit may include a switch circuit unit connected between each radio frequency port and an antenna port and a shunt circuit unit connected between each radio frequency port and a ground in order to switch a transfer path of a radio frequency signal between each radio frequency port and the antenna port.
Here, the switch circuit unit may include a transmit switch circuit unit Tx SW and a receive switch circuit unit Rx SW, wherein each of the transmit switch circuit unit and the receive switch circuit unit may include a plurality of semiconductor switches.
In the existing radio frequency switch circuit, the switch circuit unit has a structure in which a plurality of transistors are stacked in order to prepare against application of a signal having a higher level than a breakdown voltage of a single transistor.
In the structure in which the plurality of transistors are stacked, since a high voltage higher than a rated voltage is divided and applied to each of the plurality of transistors, a voltage applied to one transistor becomes low, such that the transistor may be protected from the high voltage.
In the existing radio frequency switch circuit as described above, a gate signal Vg lower or higher than a threshold voltage Vth of a transistor is provided to gates of each of the transistors included in the transmit switch circuit unit and the receive switch circuit unit, such that the transistors may be controlled in a turned-on state or a turned-off state. This gate signal may be provided from a base band chipset.
Each of the switch circuit unit and the shunt circuit unit of the existing radio frequency switch circuit has used an N-channel metal oxide semiconductor (NMOS) transistor having relatively excellent electron mobility.
However, a breakdown voltage of a 0.18 μm NMOS transistor is 3.5V, and in the case in which the 0.18 μm NMOS transistor is used as a switch as in the radio frequency switch circuit, several NMOS transistors may be stacked in a stack structure in order to withstand high power of the GSM. For example, since the shunt circuit unit has signal power of 24V as a peak voltage Vpeak in an output of 35 dBm, about eight stacked NMOS transistors should be connected to each other in series in order to appropriately disperse a voltage. As the number of stacked NMOS transistors increases as described above, loss on a signal path increases, such that overall performance of the switch is deteriorated.
A need exists for providing a radio frequency switch which decreases signal loss by decreasing the number of stacked semiconductor switches in a shunt circuit.